The present invention relates to thermoformable, multilayer acrylonitrile-butadiene-styrene (ABS) resin films and equipment liners. More particularly, the present invention relates to thermoformable, multilayer ABS films and thermoformed equipment liners obtained therefrom which are used with foamed-in-place insulation.
Acrylonitrile-butadiene-styrene resins comprise three monomeric building blocks--acrylonitrile, butadiene, and styrene--which allow for variation in properties such as chemical resistance, heat stability, impact resistance, and toughness, rigidity, and processing ease, depending on the percentages of the three major components therein and the additives used. In addition to providing useful properties to the finished products, ABS resins can be easily processed to finished parts such as by coextrusion, sheet extrusion, thermoforming, blow molding, profile extrusion, and injection molding. Because of its versatility, ABS is used in a wide variety of applications, such as equipment liners, in that it provides strong, durable shielding in many environments. Typical equipment liners include automotive interior trim, business machine housings, refrigerator liners, dishwasher liners, and appliance housings. ABS is often the material of choice for its balance of strength, toughness (impact resistance), appearance (gloss and color), chemical resistance, processability, and price. For example, this balance of properties makes ABS extruded sheets the material of choice for thermoformed equipment liners such as the interior food compartments and door liners of refrigerators. Other major end uses of ABS thermoformed extruded sheet include dishwasher liners and interior and exterior parts for trucks, autos, boats, and mobile homes.
ABS provides deep draw capability for thermoforming operations, strength and toughness for durability in assembly and use, high gloss, and chemical resistance to items such as food. Sheet extrusion grades of ABS are produced as low, medium, or high impact resins with various gloss levels ranging from high gloss to matte (low gloss). In many end uses, such as refrigerator liners, the ABS is exposed to foamed-in-place insulation during assembly. Foamed-in-place insulation typically generates a rush of blowing agent so as to foam the material (polyurethane). This rush of blowing agent passes through the conventional ABS layers, causing embrittlement and surface cracks. It is believed that the blowing agents utilized for the foamed-in-place insulation, particularly fluorohydrocarbons, degrade the ABS liner when they penetrate the liner, causing it to crack, despite the chemical resistance and impact resistance of ABS. Methods for improving the resistance of ABS resin to these blowing agents often result in the loss of some advantages of ABS resin. It is desirable to provide an equipment liner based on ABS resin which is more resistant to degradation caused by foamed-in-place insulation which maintains the advantages of ABS resins.